(45a) Synthesis and Characterization of Pt-Sn-Pd/C Catalysts for Ethanol Electro-Oxidation Reaction

Direct ethanol fuel cells (DEFC) have attracted much attention for power generation as ethanol offers higher theoretical energy density (8 kWh/kg) with less toxicity compared to methanol (6.1 kWh/kg). Also, ethanol can be easily produced in large quantities by chemical or bio processes. However, the slow reaction kinetics of ethanol electro-oxidation (EOR) on the Pt catalysts at the anode poses serious challenges in implementing the commercialization of DEFC. This has motivated considerable effort to develop alternative anode catalysts by alloying of Pt with other metals, and among the various alloying elements, Sn has shown the best promoting effect on EOR. We present here the preparation of carbon-supported Pt-Sn-Pd electrocatalysts by the borohydride reduction method and their characterization for ethanol electro-oxidation reaction. Pd is an interesting element as it exhibits catalytic properties different from that of Pt despite similar physical properties (e.g., atomic size, crystal structure, and electronic configuration). For example, while Pd is inactive for the methanol and ethanol electro-oxidation reactions, it exhibits higher activity for formic acid electro-oxidation in acid medium compared to Pt. Also, Pd is known to exhibit higher tolerance to CO and methanol compared to Pt. The Pt-Sn-Pd/ C electrocatalysts synthesized are chemically and structurally characterized, and a uniform dispersion of the metal nanoparticles on the carbon support with the intended compositions has been confirmed by EDS, TGA, and TEM analysis. However, XRD analysis reveals that the degree of Sn alloying is much lower than that intended, and most of the Sn may exist as oxide phases. Various electrochemical tests including CV, chronoamperometry, COad stripping, and EIS have been performed to compare the EOR activities of the catalysts. Among the various catalyst compositions investigated, the Pt-Sn-Pd/C (1 : 0.75 : 0.25) catalyst exhibits the highest EOR activity, followed by the Pt-Sn-Pd/C (1 : 0.5 : 0.5) and Pt-Sn/C (1 : 1) catalysts. From the electrochemical data, it is seen that the oxide phases have a promoting effect on EOR and the incorporation of a small amount of Pd into Pt-Sn/C further enhances the EOR activity.